The overall objective of the research is to define the molecules which mediate the attachment of actin to non-muscle cell membranes. To accomplish this, I am studying the way in which actin interacts with lymphocyte membranes and with the membrane of intestinal epithelial cell brush border microvilli. It has been proposed by other workers that alpha-actinin might mediate the association of actin with cell membranes. In the brush border system I have recently demonstrated that this hypothesis is incorrect. The interaction of actin with the cell membrane is effected by one or more of 3 actin binding proteins isolated from the brush border. None of these is alpha-actinin. In fact, isolated brush border and microvilli do not contain a molecule homologous to alpha-actinin. Concurrently I have demonstrated that the epithelial cell indeed does contain alpha-actinin but that this molecule is restricted to the junctional complex region of the cell. Characterization of the actin binding proteins is in progress. With respect to actin-lymphocyte membrane interactions, I have rigorously defined the presence of actin on the external surface of 40% of mouse mementeric lymph node cells. Studies are in progress to determine the origin of this actin, its physical form, its function, and its association with specific membrane proteins.